基本的光照计算公式.docVIP

基本的光照计算公式The Basic Lighting Model ?????OpenGL and Direct3D provide almost identical fixed-function lighting models. In our example, we will use a simplified version that we will refer to as the Basic model. The Basic model, like the OpenGL and Direct3D models, modifies and extends the classic Phong model. In the Basic model, an objects surface color is the sum of emissive, ambient, diffuse, and specular lighting contributions. Each contribution depends on the combination of the surfaces material properties (such as shininess and material color) and the light sources properties (such as light color and position). We represent each contribution as a?float3?vector that contains the red, green, and blue color components. This high-level equation describes the Basic model mathematically: surfaceColor?=?emissive?+?ambient?+?diffuse?+?specular The Emissive Term ?????The emissive term represents light emitted or given off by a surface. This contribution is independent of all light sources. The emissive term is an RGB value that indicates the color of the emitted light. If you were to view an emissive material in a completely dark room, it would appear to be this color. The emissive term can simulate glowing. Figure 5-2 illustrates the emissive term conceptually, and Figure 5-3 shows a rendering of a purely emissive object. The rendering is understandably boring, because the emissive color is the same all over the object. Unlike in the real world, an objects emissive glow does not actually illuminate other nearby objects in the scene. An emissive object is not itself a light source—it does not illuminate other objects or cast shadows. Another way to think of the emissive term is that it is a color added after computing all the other lighting terms. More advanced global illumination models would simulate how the emitted light affects the rest of the scene, but these models are beyond the scope of this book. Figure 5-2 The Emissive Term Figure 5-3 Rendering the Emissive Term